If they are non-renewing for an unsigned app, you should be able to contact them and get that resolved. If you don't want to stay with them, I would still finish the term and move on to a different insurer.
Switching insurance companies won't necessarily raise your rates as long as it doesn't result in a lapse in coverage. Accidents and violations can stay on your record for up to five years, so your past infractions from six years ago should not affect your rates.
It's unlikely the freezing of your credit caused your premium to change - as freezing it doesn't affect your score and that's the only way your premium would adjust. Premiums, as a whole, have increased in 2018.